Thank you, BrockleyJohn, for this module!
I have made a few changes to the file 'catalog/includes/modules/payment/quickpay_advanced.php', as I got a few errors in OSCommerce Phoenix 18.104.22.168 (I am aware that the module was not made for this version, which likely explains the errors!
Most errors were undefined constants, due to Phoenix not having the database_tables.php, and a few due to typos. One error though, caused a problem when customers got to the payment-site, cancelled and then altered their order before returning and finishing the order. In these instances, the 'admin/orders.php' showed the original order, while the payment was for the new one - I had to call a few customers, asking them what they actually wanted, before I convinced myself that I should look at the code.
I am not an experienced coder, so I might have done something terrible! Testing went fine, and this version is now live on our shop. One fault I have seen, and might get arround to fix, is that the ability to switch between 'before' and 'normal' now is gone, and all orders are created 'before'. I know why this is happening, and might be able to fix it.
Anyway, enough babbling - here's the file